1. Field of the Invention
The present invention relates to a film forming apparatus and a film forming method for performing a film forming process on a substrate in a reduced-pressure environment using a vacuum pump and a vacuum chamber, and especially relates to a physical vapor deposition apparatus and a physical vapor deposition method for forming a film by causing a film forming material emitted from a target to react with a reactive gas by use of a shield board included in a vacuum chamber.
2. Description of the Related Art
In recent years, there has been a tendency to apply a sputtering technique to metallic compounds such as titanium nitride and the like to be used for electrodes of a ferroelectric capacitor of a nonvolatile semiconductor memory circuit (FeRAM: Ferroelectric Random Access Memory) using, for example, a ferroelectric material, since the sputtering technique can achieve high purity and excellent control of film thickness. In the application of the sputtering technique, a so-called “reactive sputtering” technique is often used in which desired metallic compounds are obtained by sputtering a target of a simple metallic substance with an inert gas such as argon and then causing emitted metallic particles to react with a reactive gas such as nitrogen or oxygen. In this technique, a reactive gas, e.g. oxygen or nitrogen, is introduced into a vacuum chamber together with a sputtering gas (e.g. argon), molecules of the reactive gas and metallic particles emitted from the target through the sputtering are caused to react with each other, and thereby a thin film of generated reaction compounds is formed on a substrate.
FIG. 14 is a schematic diagram showing a conventional reactive sputtering apparatus. Such an apparatus is disclosed in Japanese Patent Application Publication No. 2009-200405, and is capable of depositing metallic compounds such as titanium nitride (TiN), iridium oxide (IrOx) or the like through reactive sputtering.
This apparatus includes exhaust means (not shown) such as an unillustrated turbo-molecular pump or the like connected to a vacuum chamber 301 formed of stainless or the like, and the vacuum chamber 301 is capable of maintaining a high-vacuum environment with a pressure of 1×10−8 Pa, for example. Moreover, the vacuum chamber 301 includes a stage 302 for holding a process-target substrate 303, and a film forming process is performed on the process-target substrate 303 placed on the stage 302.
A target 305 is formed of a pure substance or compounds of a film forming material. An unillustrated DC power supply is connected to the target 305 so that a voltage can be applied to the target 305. The target 305 is disposed in isolation from the vacuum chamber 301. Further, an unillustrated magnet is provided so that a magnetic filed can be applied to a surface of the target 305. Here, the target 305 is disposed on a packing plate 304.
Gas introduction means 314 and 315 each include flow control means such for example as a mass-flow controller, and a valve and the like. In the gas introduction means 314 and 315, means 314 for supplying a reactive gas such as nitrogen and means 315 for supplying a sputtering gas such as argon, for example, are connected together, and are configured to introduce the reactive gas and the sputtering gas into the vacuum chamber 301. The gas introduction means 315 introduces the sputtering gas, and the gas introduction means 314 introduces the reactive gas such as nitrogen. When the DC power supply inputs power to apply a negative voltage to the target 305, magnetron discharge is caused with the magnet.
Through the magnetron discharge, the sputtering gas is turned into a plasma near the target 305, and the positive ions of the plasma are accelerated by the target 305 having the negative voltage and thereby collide with the target 305. This collision of the positive ions causes atoms, molecules and the like to be emitted from the target 305, and the emitted atoms react with the reactive gas simultaneously introduced by the gas introduction means 314 to generate metallic compounds. The metallic compounds thus generated reach a surface of the substrate 303 facing the target 305. In this way, a desired film is formed on the substrate 303.
For example, by using iridium for the target 305 and an oxygen (O2) gas as the reactive gas 314, an iridium oxide (IrOx) film, which is a ferroelectric substance, is formed on the substrate 303. An O2 gas concentration meter 311 for measuring the concentration of O2 of the O2 gas is connected to the vacuum chamber 301 thorough a pipe 312. The data on the O2 concentration of the O2 gas measured by the O2 gas concentration meter 311 is transmitted to a control unit 313 electrically connected with the O2 gas concentration meter 311.
In the above-described apparatus, sputtered film is scattered around and deposited on the entire area of the vacuum chamber 301 as well as the substrate. In order to prevent particles from occurring in the film forming step, a shield board 306 needs to be provided to trap the scattered film and avoid the film from coming off easily. The shield board 306 is processed by blasting or the like so as to have a rougher surface than that of a base material, and is configured to avoid the film attached to the shield board 306 from easily coming off from the shield board 306. Further, the shield board 306 is configured to be reusable in a way that when a certain amount of film is deposited on the shield board 306, the shield board 306 is detached and then separately processed by blasting or the like to remove the deposited film. Moreover, the shield board 306 is configured to form a shield-inside space 318 and a shield-outside space 319 by surrounding a space from near the target 305 to the stage 302. The shield-inside space 318 and the shield-outside space 319 encircle the target in the film forming chamber 301. The shield board 306 prevents the film from attaching to wall surfaces of the shield-outside space 319.
Here, the reactive gas and the sputtering gas introduced into the shield-outside space 319 by the gas introduction means 314 and 315 are supplied to the shield-inside space 318 through an opening 320 in the shield board 306 while being discharged from the shield-inside space 318 to the shield-outside space 319 at the same time.
Since the concentration of the reactive gas 315 significantly affects the film quality, the means 311 for monitoring the concentration of the reactive gas is provided near the process-target substrate 303 in the shield-inside space 318 as described above. It is described that quality control of the film is achieved at a low cost by controlling the flow rate of the reactive gas supplied to the gas introduction means 314 so that the concentration of the reactive gas would be kept constant near the process-target substrate.
Meanwhile, FIG. 15 is a schematic diagram showing another conventional reactive sputtering apparatus. Such an apparatus is disclosed in Japanese Patent Application Publication No. Hei 05-247639. This apparatus includes a shield board 406 defining a sputtering space in a vacuum chamber 401, and is configured to form a thin film on a surface of a wafer 408 placed on a wafer stage 407 in the vacuum chamber 401, by depositing metallic particles emitted from a sputtering target 405 disposed in an upper part of the vacuum chamber 401. Further, this apparatus includes a reactive gas introduction port 403a configured to introduce a reactive gas such as argon directly into the space defined by the shield board (shield) 406, and a manometer 404 capable of directly measuring the pressure in the space defined by the shield board 406. In FIG. 15, 401a denotes a discharge port, 401b denotes a wafer receiving port, 402a denotes a gate valve, 402 denotes a cryopump, and 406a denotes an opening in the shield board 406. In the case of this apparatus, a reactive-gas discharge port 410 is formed in the shield board 406, and is configured to exhaust the reactive gas directly into a shield-inside space 418. It is possible to adjust the flow rate of the reactive gas being introduced, while monitoring the pressure in the shield-inside space 418 by use of the manometer 404 for measuring the pressure.
However, in each of the above-described two apparatuses, the shield board 306 or 406 needs a replacement process on a regular basis in order to remove a film attached to the surface of the shield board 306 or 406. In the replacement process, the shield board 306 or 406 is detached from the gas introduction means 314 and 315 or 403a at a connection part. In general, to enable reuse of the shield board 306 or 406 for a certain number of times, a recovery process is performed in which an attaching film is removed by a chemical or physical force after the shield board is removed. In this recovery process, it is difficult to remove only the attached film without applying any stress to the shield board 306 or 406 at all, and the shield board 306 or 406 itself is inevitably changed in shape and size through chemical etching or a physical removing process.
Moreover, even if no recovery process is involved, the shield board 306 or 406 is detached and then attached again for the purpose of replacing a used-up target or the like. This operation may cause a change in attachment position of the shield board 306 or 406 or in clearance between the target 305 or 405 and the shield board 306 or 406. It is also natural that the attachment position of the shield board 306 or 406 varies between different chambers configured of the same components.
In the case of such a reactive sputtering apparatus as disclosed in Japanese Patent Application Publication No. 2009-200405, a change in shape or attachment position of the shield board 306 also causes a change in size of the opening 320 between the shield-inside space 318 and the shield-outside space 319. This may cause a change in flow rate of the reactive gas supplied to the shield-inside space 318 and the shield-outside space 319. In order to make calibration for this, the flow rate itself of the reactive gas 314 may be adjusted so that the concentration of the reactive gas in the shield-inside space 318 can be at a predetermined value. However, this also changes the flow rate of the reactive gas introduced into the shield-outside space 319, and consequently may affect the distribution of the reactive gas in the shield-inside space 318. In other words, a change in pressure in the shield-outside space 319 changes the rate and the distribution of the flow of the reactive gas from the shield-inside space 318 to the shield-outside space 319, which may consequently affect the film quality and the distribution obtained through the reactive sputtering.
By contrast, such a reactive sputtering apparatus as disclosed in Japanese Patent Application Publication No. Hei 05-247639 is configured to let the introduced reactive gas from the introduction means 403a directly into the shield-inside space 418. Here, in order to introduce the whole amount of the reactive gas introduced by the gas introduction means 403a into the shield-inside space 418, the gas inlet part 410 needs to be airtight from the shield-outside space 419.
However, an apparatus such as a reactive sputtering apparatus is likely to be negatively affected by an out gas from a member. Accordingly, for a supply path of the reactive gas, using a resin sealing material or the like is not preferable, and using a technique such as welding or solder bonding significantly reduces efficiency in detaching the shield board 406. In addition, since changes in shape and size as a result of recovering the shield board 406 occur randomly, it is difficult to control the amount of the reactive gas leaking from the gas inlet part 410 to the shield-outside space 419. Hence, this apparatus has a similar problem as that of Japanese Patent Application Publication No. 2009-200405 in terms of reproducibility of the film quality of the reactive sputtering in association with the recovery of the shield board 406. No technique which can solve this problem is known so far as long as the inventors of the present invention know.